The present invention relates to Surface Acoustical Wave (SAW) tapered transducers and a dispersive reflective array. The transducer is shown in conjunction with dispersive array that has an electrode pattern which reduces insertion loss and electrode resistance and which allows the electrodes to be connected in series electrically, in order to raise the acoustic impedance of the device.
Wide-band linear phase SAW filters using slanted finger transducers are described in "Wide Band Linear Phase SAW Filters Using Apodized Slanted Finger Transducers" by P. M. Naraine and C. K. Campbell in the 1983 IEEE Ultrasonic Symposium Proceedings, pages 113-116. The slanted finger interdigital transducer structure described in this article employed straight slanted fingers which emanated from a common focal point, in an effort to yield a flat amplitude response across a passband. Apodization of the device was derived from a computer optimization routine to compensate for the inherent negative amplitude slope of an unapodized slanted finger transducer, so that the external amplitude equalization circuits were not needed.
A subsequent article entitled "Improved Modeling of Wide-Band Linear Phase SAW Filters Using Transducers with Curved Fingers" by N. J. Slater and C. K. Campbell was published in the IEEE Transactions on Sonics and Ultrasonics, Vol. SU-31, No. 1 January 1984, pages 46-50. The authors of this work describe a wide band linear phase SAW filter in which slanted fingers such as those shown in the Naraine and Campbell article have been curved to obtain a flatter frequency response for delay line applications.
The present invention involves transducers with curved fingers which are, in particular, hyperbolically tapered in conjunction with a dispersive reflective array to provide an improved SAW dispersive filter. The transducers of the present invention also utilize configurations which reduce the insertion loss and allow for the acoustic impedance to be increased by a unique finger design.
A transducer constructed in accordance with this invention is shown in U.S. Pat. No. 4,635,008 issued Jan. 6, 1987 to the inventor of this invention which is assigned to the assignee of this invention, the Unisys corporation, the successor of the Sperry Corporation.